Conventional overhead-valve internal-combustion engines incorporate a cylinder head in which the intake and exhaust valves are movably mounted and oriented such that the valve stems extend from the valve head in a direction generally away from the top of the cylinder bore. Push rods, engaging valve lifters activated by a cam shaft located in the cylinder section of the engine, extend into the cylinder head alongside the valve stems.
Between each valve stem and its corresponding push rod is a rocker arm pivotally mounted on a rocker-arm stud connected to the cylinder head. The rocker arms are maintained in place by a rocker-arm adjusting nut, whereby a frictional movement occurs between a pivot ball washer and the inner surface base of the rocker arm. The push rod has a bottom end which rests on the cam shaft and moves move up and down as the cam shaft rotates. The up and down motion of the push rod causes the rocker arm to rock back and forth which, in turn, causes the valve which is connected to the rocker arms to also move up and down. When the valve moves up, it seals the combustion chamber thereby stopping the fuel from entering through the engine intake port or leaving through the exhaust port. Thus, it can be seen that it is of the utmost importance that the rocker arm be properly adjusted to enable the valve to completely seal the combustion chamber.
The rocker-arm studs are conventionally attached at their lower end to the cylinder head by either a tight press-fit into a corresponding bore or by threading. The upper end of the rocker arm stud is usually threaded and is received loosely through an elongated hole in the bottom of the rocker arm. Between a spherical bearing surface inside the rocker arm and the upper threaded end of the rocker arm stud is located the pivot ball washer. A locking-type adjusting nut is threaded onto the upper end of the rocker arm stud above the pivot ball washer. This nut is used to adjust the valve lash by moving the rocker arm pivot point up or down by turning the adjusting nut with respect to the fixed rocker arm stud to a selected position.
One of the fundamental problems associated in the manipulation of a rocker arm adjusting nut is in the method and tools required to make the adjustment. In these prior art designs, the wrench used to make the adjustment can easily slip over the body of the nut adding to the difficulty in making a final adjustment. By using the twelve-point rocker-arm adjusting nut of the instant invention in combination with a corresponding twelve-point wrench, the problem of wrench slippage is virtually eliminated and the twelve-point design also prevents the wrench from vibrating off the nut when adjustments are made with the engine running.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however the following U.S. patents are considered related:
______________________________________ U.S. Pat. No. INVENTOR ISSUED ______________________________________ 4,856,467 Kronich 15 August 1989 4,784,095 Golding et al 15 November 1988 4,561,392 Jette 31 December 1985 3,189,011 Briggs 15 June 1965 ______________________________________
The U.S. Pat. No. 4,856,467 Kronich patent discloses an adjustable valve lash train for an overhead valve engine that includes a rocker-arm stud having a threaded shank received in a threaded bore in the cylinder head. The rocker-arm stud includes a head having a spherically shaped bearing surface that engages a similar shaped bearing surface on the rocker arm and has a hexagonally shaped recess on its top surface for receiving an adjustment tool. A threaded jam nut is located above the threaded shank of the rocker arm stud for locking the threaded shank against rotation with respect to the threaded bore of the cylinder head.
The U.S. Pat. No. 4,784,095 Golding et al patent discloses a rocker arm adjusting nut particularly adaptable for use with steel rocker arms as employed in automotive engines. The nut consists of an integral unit having a hex nut, an upper collar, a bottom flange and an axially elongated body having a central portion provided with axial grooves. The upper collar and grooves in combination, deflect oil axially towards the bottom flange when the nut is in use. The enlarged mass and surface area of the nut also helps, by conduction, to dissipate temperature from the pivot ball-rocker arm interface and deflect oil towards the interface.
The U.S. Pat. No. 4,561,392 Jette patent discloses a girdle assembly for stud mounted rocker arms. The assembly is particularly adapted for use in racing engines where the valve stud structure is unified to prevent stud fatigue failure and adverse harmonics. The girdle is self aligning to the studs over a suitable range of positions, uses clamping forces developed without screws tension in the plane of the girdle and can be readily removed and replaced after being installed.
The U.S. Pat. No. 3,189,011 Briggs patent discloses a self adjusting valve actuating mechanism. The mechanism consists of an arrangement whereby the upper end of the push rod is automatically movable to and from a post having a spherical bearing head. The push rod movement varies its effective length by shifting the position of the cam surface on the cam carrier with respect to the cam follower bearing surface.
For background purposes and as indicative of the art to which the invention is related reference may be made to the following remaining patents found in the search:
______________________________________ U.S. Pat. No. INVENTOR ISSUED ______________________________________ 4,686,946 Umeda et al 18 August 1987 4,393,820 Maki et al 19 July 1983 4,314,732 Murphy 9 February 1982 3,754,539 Bandimere 28 August 1973 3,219,019 Palmer 23 November 1965 RE 24,035 Leach 12 July 1955 ______________________________________